The Coalition may get its welfare bill passed but it may do so at a cost to its relations with the House of Lords.

The Upper House repeatedly amended the welfare bill - sometimes by large majorities. Labour, crossbench and Lib Dem rebels defeated, for example, the benefits cap but there were also a significant Tory rebellion - led by the former Lord Chancellor, Lord Mackay - against reforms to the Child Support Agency.

The Coalition is attempting to prevail by asserting what is known as "financial privilege". This gives the Commons "sole rights" in respect of financial legislation that applies indivisibly to public expenditure and to the raising of revenue to meet that expenditure (PDF background here).

"It cannot be denied that we are in extremely difficult financial times, and that the government has no choice but to take measures to address the situation. Tackling the unsustainable rise in spending on benefits and tax credits, as part of the government’s overall deficit reduction strategy, is undeniably important."

Many peers have objected and not just opposition members. Former Tory MP Patrick Cormack, now enobled, said that the Commons was "overasserting" privilege. Former Social Security Secretary Lord Newton of Braintree said "real questions" were raised by ministers' behaviour.

"I respectfully suggest to my noble friend the Leader of the House that he has a duty to the House as a whole, as well as to the Government's interests. There have been a series of events that give the impression that the other place, which increasingly sends legislation up here that is not properly considered and debated, is treating this place with some contempt, not least of which is the suggestion that the Parliament Act might be used in respect of the reform of this place. I suggest to my noble friend that the time may have come for him to assert his authority as Leader of the House and have a frank chat with some of his colleagues."

Strong stuff and the former Chancellor Lord Lawson agreed:

"While the House of Commons is perfectly entitled to claim privilege, it is not compelled to do so. The constitution of this country operates by conventions. It is one of the conventions of the constitution that this is evoked very sparingly and on rare occasions. For it to be invoked promiscuously is completely contrary to the conventions of the constitution."

Defending his ministerial colleagues Lord Strathclyde insisted they had acted properly and that, as is required, the Speaker of the Commons had impartially ruled that financial privilege did apply to the welfare reforms andthat the Lords should respect that ruling.